The present invention relates to an apparatus for regulating the position of an adjustably positionable vehicle part.
A regulating apparatus disclosed in German patent document G 93 13 949.7 can be used, for example, to regulate the positioning of windows, movable roofs, or seats. It is therein suggested to provide in such an apparatus damping elements on each end of the drive shaft to accommodate possible displacement within a predetermined tolerance of the drive shaft and thereby avoid the noises arising from changes in the direction of rotation of the shaft. To this end, elastomeric elements in plate form are disposed between a drive shaft housing piece and a support plate in contact with the drive shaft. The drive shaft presses the support plate against the elastomeric elements and this serves to maintain the elastomeric elements in place. However, the occurrence of a misalignment of the drive shaft or aging of the elastomeric material can prevent this arrangement from offering an optimal seating. Moreover, such events may alter the surface pressure on the elastomeric elements whereby the operating condition of the apparatus can be undesirably influenced.
The present invention provides an apparatus for regulating the position of an adjustably positionable vehicle part which advantageously enhances the reliability of the regulation of the vehicle part to its desired adjusted position. According to one aspect of the present invention, there is provided an apparatus for regulating the position of an adjustably positionable vehicle part which includes an electric drive motor having a drive shaft which is axially displaceable within a fixed limit during driving operation of the shaft. Also, the apparatus includes a power transfer assembly having a driven member operatively connected to the drive shaft of the electric drive motor for driving movement thereby and a damping member for damping the axial displacement of the drive shaft of the electric motor in one axial direction. The apparatus also includes a housing having a chamber compatibly dimensioned with respect to the damping member for receiving the damping member therein in a press fit disposition.
The apparatus of the present invention advantageously maintains the damping member in its desired position such that aging or hardening of the damping member or pressure from a misaligned drive shaft will not displace the damping member from its desired position. Also, the single step of press fitting the damping member into the chamber eliminates the need for additional pieces to maintain the damping member in the chamber.
Another advantage of the apparatus of the present invention lies in the fact that the loading of the damping member by the drive shaft can be selected independent of the already known preloading imposed on the drive shaft in the housing. The preloading of the drive shaft is directly related to its length as produced within tolerance limits, the effects of the preloading on the drive shaft due to its length can be mitigated or eliminated by proper selection of the damping member.
The chamber preferably includes an oversurface having a rib structure which includes a plurality of ribs and the damping member distributes itself around the ribs during its press fit installation, thereby ensuring a firm seating of the damping member in the chamber. Also, the ribs are distributed in spaced manner around the circumferential periphery of the chamber and this facilitates the introduction of the damping member into the chamber.
In certain circumstances, a single rib can ensure a firm seating of the damping member.
The damping member in its uncompressed condition extends axially beyond the chamber such that the drive shaft can work in an undisturbed manner with the damping member without a transfer of vibrations of the drive shaft to the housing.
If the chamber is provided with a shoulder which is engaged by a shoulder on the adjacent axial end of the drive shaft or a shoulder on a plate intermediate the damping member and the drive shaft, this arrangement sets in a straightforward way the maximum limit to which the damping member will be compressed. The damping rubber is thereby protected during the cyclic loading whereby the aging of the damping rubber is slowed and its useful life is extended.
One beneficial feature of the apparatus of the present invention is that the ribs form spaces therebetween having a collective volume capacity sufficient to accommodate the compressed damping member fully within the chamber at the maximum compression of the damping member. The spring rate of the damping member as measured with respect to its effect on the end of the drive shaft thus substantially approaches that of an unconstrained damping member. In this situation, those influences on the spring rate produced by the press fit seating of the damping member are merely negligible.
A particularly favorable spring and damping characteristic can be obtained if the length of the damping member taken in the axial direction of the drive shaft is greater than the width of the damping member measured perpendicularly to its length. In particular, a length to width ratio greater than 1.3:1 is preferred or, even more preferably, a ratio of 1.5:1. By this approach, one achieves a very flat characteristic-force per press in wayxe2x80x94so that the influence of the damping member on the shaft is virtually independent from its preload or built in tension. In this manner, a spring rate of less than 50 Newtons per millimeter can be achieved.
The use of a soft rubber and, in particular, a rubber substantially or completely formed of N-butyl beneficially enhances the spring rate.
In the event that a plate is provided intermediate the damping member and the drive shaft, it is advantageous if the plate is retained in another chamber formed in the housing which includes projections that prevent undesired movement of the plate out of the chamber.